This invention relates to a development station for an electrographic apparatus having a magnetic brush for developing an electrostatic image wherein flow of developer material to the brush and removal of material from the brush are controlled together for starting and stopping development of the images.
In electrographic development apparatus there is a recognized need to be able to create a layer of development particles on a magnetic brush quickly in order to develop an image and to shut off the flow of development material to the brush when development of images is not desired. For example, U.S. Pat. No. 3,579,139, issued Apr. 20, 1971, discloses a developer unit having devices which control the developing action of the unit so that the action can be switched on or off rapidly. The developer unit has two brushes, and a gate adjacent one of the brushes is mounted for movement into and out of engagement with the brush to control the flow of developer material to the one brush. The second brush of the developer unit has a magnet which is rotated to interrupt flow of developer material over the second brush. The magnet and the gate are controlled by the machine programming system and can be simultaneously operated by the programming system. A mechanism for controlling formation of bristles on the brush is needed not only for applying black toner but also in color copiers where toners of two or more colors are provided to a photoconductor, and it is important to be able to rapidly start and stop any one of several development stations with accuracy to avoid overlapping of the different toners on the photoconductor.
It is also known to provide a wiper blade for scraping developer material from a magnetic brush after the developer material has passed through the development zone. Such a wiper blade can return toner-depleted developer material to a sump for replenishment of toner before the developer material is again provided to the development zone. Such wiper blades tend to have a short useful life due to constant engagement of the blade with the magnetic brush.